Method and apparatus for modulating signal waveforms in a CDMA communication system

Abstract

An improved system and method for transmitting information within a digital communication system is disclosed herein. A modulation system for use in a digital cellular communication system is described in which information is exchanged among a plurality of mobile users, via at least one cell-site, using a set of orthogonal binary codes. The modulation system allows the information carrying capacity of signal transmission on the mobile-to-cell communication link, i.e., the "reverse" link, of the communication system to be significantly improved. The modulation system receives an input information signal an generates an orthogonal sequence signal in response thereto. The orthogonal sequence signal corresponds to a selected one of a plurality of orthogonal binary chip sequences derived from a set of orthogonal binary codes. The orthogonal binary sequences are constructed such that a selected chip at a predefined sequence position within each of the orthogonal binary sequences is of the same binary value. The selected orthogonal sequence signal is combined with a control signal to provide a punctured sequence signal. This combination is performed such that the punctured sequence signal includes a control chip at the predefined sequence position having a value determined by the control signal. The punctured sequence signal may then be transmitted via a carrier signal. In a particular spread spectrum implementation, the punctured sequence signal is combined with a pseudo-noise (PN) signal in order to generate a carrier modulation signal.

We claim: 
     
       1. A modulation system for use in spread spectrum communications, comprising: means for receiving an input signal and for generating, in accordance with a value of said input signal, a first orthogonal sequence signal corresponding to one of a plurality of orthogonal binary chip sequences, each of said orthogonal binary chip sequences having a selected chip of an identical binary value located at an identical predefined sequence position;   means for combining said first orthogonal sequence signal with a control signal to generate a first punctured sequence signal, said punctured sequence signal including a control chip at said predefined sequence position having a binary value corresponding to said control signal;   means for generating a pseudo-noise (PN) signal corresponding to a predetermined PN binary sequence; and   means for combining said first punctured sequence signal and said PN signal and for providing a resultant first modulation signal.   
     
     
       2. The system of claim 1 wherein said plurality of orthogonal binary sequences are Walsh sequences. 
     
     
       3. The system of claim 2 wherein said selected chip at said predefined sequence position corresponds to a first chip of each of said Walsh sequences. 
     
     
       4. A spread spectrum communication system including a modulator for modulating a digital user information signal for transmission over a communication channel, said modulator comprising: orthogonal sequence generator means for receiving said user information signal and for generating, in accordance with a value of said user information signal, a preselected Walsh sequence included within a set of orthogonal Walsh binary sequences, each of said orthogonal binary chip sequences having a selected chip of an identical binary value located at an identical predefined sequence position;   means for combining said preselected Walsh sequence signal with a control signal to generate a first punctured sequence signal, said punctured sequence signal including a control chip at said predefined sequence position having a binary value corresponding to said control signal;   pseudorandom noise (PN) generator means for generating first and second PN signals of a code sequence different from one another; and   combiner means for receiving and combining said punctured sequence signal respectively with said first and second PN signals, and providing resultant first and second output modulation signals.   
     
     
       5. The system of claim 4 further comprising transmission means for modulating said first and second output modulation signals upon a carrier signal and transmitting said modulated carrier signal. 
     
     
       6. The system of claim 5 further including receiver means for receiving said modulated carrier signal and means for extracting said control signal therefrom. 
     
     
       7. The system of claim 6 wherein said receiver means further includes demodulator means for demodulating said modulated carrier signal using said preselected Walsh sequence. 
     
     
       8. The system of claim 7 wherein said demodulator means further includes means for generating a first despreading signal by replicating said first PN signal, and means for correlating said modulated carrier signal using said first despreading signal so as to provide a first correlated output signal. 
     
     
       9. The system of claim 8 wherein said demodulator means further includes means for generating a second despreading signal by replicating said second PN signal, and means for correlating said modulated carrier signal using said second despreading signal to provide a second correlated output signal. 
     
     
       10. The system of claim 9 wherein said means for extracting said control signal includes means for combining said first and second correlated output signals. 
     
     
       11. A method for modulating a spread spectrum information signal, comprising the steps of: generating, in accordance with a value of said information signal, a first orthogonal sequence signal corresponding to a selected one of a plurality of orthogonal binary chip sequences, each of said orthogonal binary chip sequences having a selected chip of a common predefined binary value located at a common predefined sequence position;   combining said first orthogonal sequence signal with a control signal to generate a first punctured sequence signal, said punctured sequence signal including a control chip at said predefined sequence position having a binary value corresponding to said control signal;   generating a pseudo-noise (PN) signal corresponding to a predetermined PN binary sequence; and   combining said first punctured sequence signal and said PN signal so as to provide a resultant first modulation signal.   
     
     
       12. The method of claim 11 wherein said step of generating a first orthogonal sequence signal includes the step of generating a first Walsh sequence. 
     
     
       13. The method of claim 12 wherein said selected chip at said predefined sequence position corresponds to a first chip of each of said Walsh sequences. 
     
     
       14. A method for transmitting a digital user information signal over a communication channel, said method comprising the steps of: generating, in accordance with a value of said digital user information signal, a preselected Walsh sequence included within a set of orthogonal Walsh binary sequences, each of said orthogonal binary chip sequences having a selected chip of an identical binary value located at an identical predefined sequence position;   combining said preselected Walsh sequence signal with a control signal to generate a first punctured sequence signal, said punctured sequence signal including a control chip at said predefined sequence position having a binary value corresponding to said control signal;   means for generating first and second pseudorandom noise (PN) signals of a code sequence different from one another; and   receiving and combining said first punctured sequence signal respectively with said first and second PN signals, and providing resultant first and second output modulation signals.   
     
     
       15. The method of claim 14 further comprising the steps of: modulating said first and second output modulation signals upon a carrier signal; and   transmitting said modulated carrier signal.   
     
     
       16. The method of claim 15 further including the step of receiving said modulated carrier signal and extracting said control signal therefrom. 
     
     
       17. The method of claim 16 further including the step of demodulating said modulated carrier signal using said preselected Walsh sequence. 
     
     
       18. The method of claim 17 wherein said step of demodulating includes the steps of: generating a first despreading signal by replicating said first PN signal; and   correlating said modulated carrier signal using said first despreading signal so as to provide a first correlated output signal.   
     
     
       19. The method of claim 18 wherein said step of demodulating further includes the steps of: generating a second despreading signal by replicating said second PN signal; and   correlating said modulated carrier signal using said second despreading signal so as to provide a second correlated output signal.   
     
     
       20. The method of claim 19 wherein said step of extracting said control signal includes the step of combining said first and second correlated output signals. 
     
     
       21. A digital communication system, comprising: means for receiving an input signal and for generating, in accordance with a value of said input signal, a first orthogonal sequence signal corresponding to one of a plurality of orthogonal binary chip sequences, each of said orthogonal binary chip sequences having a selected chip of an identical binary value located at an identical predefined sequence position;   means for combining said first orthogonal sequence signal with a control signal to generate a first punctured sequence signal, said punctured sequence signal including a control chip at said predefined sequence position having a binary value corresponding to said control signal; and   a transmitter for modulating a carrier signal using said punctured sequence signal, and for transmitting the resulting modulated carrier signal.   
     
     
       22. The system of claim 21 wherein said plurality of orthogonal binary sequences are Walsh sequences. 
     
     
       23. The system of claim 22 wherein said selected chip at said predefined sequence position corresponds to a first chip of each of said Walsh sequences. 
     
     
       24. The system of claim 23 further including a receiver for receiving said modulated carrier signal, and for extracting said control signal therefrom. 
     
     
       25. The system of claim 24 wherein said receiver means further includes demodulator means for demodulating said modulated carrier signal using said preselected Walsh sequence. 
     
     
       26. A method for communicating a digital information signal over a communication channel comprising the steps of: generating, in accordance with a value of said digital information signal, a first orthogonal sequence signal corresponding to a selected one of a plurality of orthogonal binary chip sequences, each of said orthogonal binary chip sequences having a selected chip of common binary value located at a common predefined sequence position;   combining said first orthogonal sequence signal with a control signal to generate a first punctured sequence signal, said punctured sequence signal including a control chip at said predefined sequence position having a binary value corresponding to said control signal; and   combining said first punctured sequence signal and a PN signal so as to provide a resultant first modulation signal.   
     
     
       27. The method of claim 26 wherein said step of generating a first orthogonal sequence signal includes the step of generating a first Walsh sequence. 
     
     
       28. The method of claim 27 wherein said selected chip at said predefined sequence position corresponds to a first chip of each of said Walsh sequences.